ected by variations of the
barometric pressure, and is simple and easy to fit up. It consists of a
thermometer with an elongated glass bulb 5/8 inch diameter and 3 inches
long. The stem of the thermometer is 5 inches long and 1/8 inch to 3/16
inch internal diameter. One and a half inch from the top of the stem is
fused in at right angles a piece of glass tube, 1 inch long, of the same
diameter as the stem, so as to form a T. A piece of glass tube (A), about
7/16 inch external diameter and 1-1/2 inch long, is fitted at one end with
a short, sound cork (C, Fig. 50). Through the centre of this cork a hole
is bored, so that the stem of the thermometer just fits into it. The other
end of this glass tube is closed by a tightly fitting cork, preferably of
indiarubber (I), which is pierced by a fine bradawl through the centre.
Into the hole thus made is forced a piece of fine glass tube (B) 3 inches
long, and small enough to fit loosely inside the stem of the thermometer.

[Footnote A: _Chemical Soc. Jour._, 1876, i. 24.]

The thermometer is filled by pouring in mercury through a small funnel
until the level of the mercury (when the thermometer is at the desired
temperature) is about 1-1/2 inch below the T. The piece of glass tube A,
closed at its upper extremity by the cork I, through which the fine glass
tube B passes into the stem of the thermometer, is now filled by means of
the perforated cork at its lower extremity on the stem of the thermometer.
The gas supply tube is attached to the top of the tube A, the burner to
the T, so that the gas passes in at the top, down the fine tube B, rises
in the space between B and the inside wall of the stem of the thermometer,
and escapes by the T. The regulator is set for any given temperature by
pushing the cork C, and consequently the tubes A and B, which are firmly
attached to it, up or down the stem of the thermometer, until the
regulator just cuts off the gas at the desired temperature.

[Illustration: FIG. 49.--PAGE'S REGULATOR.]

[Illustration: FIG. 50.--PAGE'S GAS REGULATOR, SHOWING BYE-PASS AND
CUT-OFF ARRANGEMENT.]

As soon as the temperature falls, the mercury contracts, and thus opens
the end of the tube B. The gas is thus turned on, and the temperature
rises until the regulator again cuts off the gas. In order to prevent the
possible extinction of the flame by the regulator, the brass tube which
carries the gas to the regulator is connected with the tube which brings
t